Production of ethylene



United States Patent 3,278,629 PRODUCTION OF ETHYLENE Robert L. Hartnett, Texas City, Tex., assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Apr. 21, 1964, Ser. No. 361,589 3 Claims. (Cl. 260-6833) This invention relates to an improved process for the production of olefins from saturated hydrocarbons. More particularly, it relates to the production of ethylene from ethane.

It is well known that olefins can be obtained by thermal decomposition of petroleum-derived hydrocarbons. Ethylene can be obtained, for example, by thermal conversion of light saturated hydrocarbons such as ethane and/ or propane. However, in such a process the gaseous conversion product contains, in addition to the desired ethylene, significant amounts of other products such as methane, propylene, acetylene, butenes, and the like. In order to recover the ethylene in sufficiently pure form for its utilization, the gaseous thermal conversion product must be processed by fractionation in a series of steps requiring fairly elaborate equipment and time consuming operations. Furthermore, non-gaseous hydrocarbons such as oils and tars and normally cyclic hydrocarbons are formed simultaneously with the ethylene. Provision must-be made for removal of such contaminants because they lead to fouling of the apparatus and equipment. Thus, despite extensive studies which have been made on cracking of light hydrocarbons to produce ethylene, there are still some disadvantages in commercial production by this method.

' Some of the problems inherent in the production of ethylene by cracking techniques can be obviated by producing this hydrocarbon in a relatively pure state by catalytic dehydrogenation of ethane. However, the art has thus far failed to provide a continuous process for the dehydrogenation of ethane to ethylene which is not subject to a number of drawbacks. Known catalysts for the dehydrogenation suffer from deficiencies in that they ether result in low conversion to dehydrogenation products or to low yields of ethylene or are deficient in both respects. Prior art catalysts, too, become readily fouled with carbon deposits which render them ineffective in the dehydrogenation process and necessitate frequent and sometimes expensive regeneration. The advantages of a process wherein conversion of ethane to ethylene can be effected with fewer operational steps and less byproduct formation are, therefore, immediately obvious.

It is an object of the present invention to provide a process wherein ethane can be readily converted to ethylene in a relatively simple process and with comparatively little loss to non-useful by-products. Other objects and advantages of the invention will become apparent from the following description.

According to the present invention, a mixture of ethane, hydrogen chloride and oxygen or air is contacted at an elevated temperature with activated alumina to produce an effluent gas mixture from which ethylene can be recovered in good yield. Only small amounts of chlorinated by-products are produced which are readily separable from ethylene, fewer steps are required for recovery of ethylene than are employed in the prior art and the hydrogen chloride employed can be continuously recycled in the process.

Patented Oct. 11, 1966 ICC The invention is illustrated in the following examples which, however, are not to be construed as limiting it in any manner whatsoever.

EXAMPLE 1 A tubular reactor about 6 ft. long and 60 mm. in diameter wrapped with nichrome wire for heating and covered with asbestos insulation was employed as the reactor. A thermowell containing thermocouples for measuring temperatures was centrally positioned in the reactor extending throughout its length. Approximately 1000 g. of activated alumina (marketed by Aluminum Company of America under the trade designation F-l) was charged to the reactor and fluidized by passing nitrogen up through it while the reactor was brought up to reaction temperature. Thereafter, hydrogen chloride and oxygen at approximate rates of 0.06 and 0.03 s.c.f.m. (standard cubic feet per minute), respectively, were passed through rotameters into a common manifold where they were mixed and from which they were then introduced into the bottom inlet of the reactor to contact the fluidized catalyst maintained at a temperature from about 500 C. to about 600 C. Ethane, at a rate of about 0.06 s.c.f.m., was fed separately through a rotameter and injected simultaneously into the fluidized catalyst in the reactor at a point about 5 inches above the bottom inlet As the reactants were introduced, the flow of nitrogen was appropriately reduced so that the velocity of the entering gaseous reactants helped to maintain the catalyst in the fluidized state. Contact time was approximately 4.7 seconds.

Effluent gases from the top of the reactor were passed directly into a vapor phase gas chromatograph for analysis. From the analysis of the reaction product collected at various temperature levels, total conversion of ethane, conversion of ethane to ethylene, .and yields of ethylene were calculated. Results are presented in Table 1 below.

Table 1 Total Conv. to Yield of CzHt (32 4, 2 4,

Temperature, C. Oonv., percent percent percent EXAMPLE 2 The experiment of Example 1 was repeated with the fluidized catalyst being maintained at a temperature from about 530 C. to about 590 C. and the contact time increased to 7.5 seconds by using 2000 g. of catalyst in the reactor. Results are tabulated below.

Table 2 Total Conv. to Yield of Temperature, C. Conv., percent percent percent EXAMPLE 3 The reactor of Example lwas charged with 1500 g. of activated alumina and, following the procedure in that example, hydrogen chloride and oxygen were fed into the bottom of the reactor at rates of 0.135 s.c.f.m. and 0.030 s.c.f.m., respectively, while ethane was injected at a point about 10 inches above the bottom inlet at a rate of 0.135 s.c.f.m. into the fluidized alumina. Contact time was approximately 7.2 seconds and the mole ratio of ethane to hydrogen chloride to oxygen was 1:1:0.22. The temperature in the catalytic reaction zone was maintained between 500 and 600 C. Data obtained by calculation from the effluent gas analyses at the several temperatures in this range are presented below.

Table 3 Total Conv. to Yield of Temperature, C. Conv., percent percent percent EXAMPLE 4 The experiment of Example 3 was repeated except that flow rates of ethane, hydrogen chloride and oxygen Were adjusted at 0.155, 0.077, and 0.0385 s.c.f.m., respectively, to provide a mole ratio of these reactants of 2:1:0.5 and .a contact time of 7.2 seconds. Results obtained by calculations based on chromatographic analysis of the prod- The experiment of Example 3 was again repeated with feed rates of ethane, hydrogen chloride, and oxygen maintained at 0.116, 0.116, and 0.0385, respectively, to provide a mole ratio of ethane, hydrogen chloride and oxygen of 1:1:0.3 and a contact time of 7.2 seconds. Conversions and yields obtained under these conditions are tabulated below.

Table 5 Total Conv. to Yield of CzHu C2114, C2H4, Temperature, C. Conv., percent percent percent It is readily apparent that various modifications of reaction conditions given in the examples can be made without departing from the scope of the invention. In the preferred embodiment of the invention, the activated alumina catalyst is employed in the fluidized or pseudo liquid state. It is maintained in a fluid or suspended state by the gaseous reactants themselves or, optionally, by the use of an additional inert gas introduced from an outside source. The use of a fixed bed operation, however, is not precluded.

The preferred method of introducing the reactants is that which is exemplified, that is, the hydrogen chloride and oxygen or air are introduced into the bottom of the reactor while ethane is injected at a point somewhat above the bottom inlet point. The point of ethane injection is suitably located at a distance of from about 5% to about 20% of the reactor length above the inlet of the other reactants. Optimum results are obtained with the ethane being injected at a point from about 7% to about 10% of the reactor length above the bottom inlet. The reaction may be carried out by mixing the ethane, hydrogen chloride and oxygen or air and passing the mixture into the reactor, or by introducing air or oxygen into a mixture of ethane and hydrogen chloride. These latter methods are, however, much less satisfactory than the preferred one. Precaution should be taken to avoid mixing ethane and oxygen in the absence of hydrogen chloride to prevent creation of possible hazardous conditions.

As is evident from the examples, the relative proportions of the reactants may vary considerably. Ratios of ethane to hydrogen chloride to oxygen varying from 1:0.5:0.2 to 1:2:1 can be used. It is understood that the oxygen for the reaction may, of course, be supplied in the form of air and when air is used the mole ratio of ethane to hydrogen chloride to air may vary from 1:0.5:1 to 1:2:5. Preferably, the mole ratio when oxygen is employed is maintained at about 1:1:0.3 and correspondingly at 12111.5 when air is used. Since little hydrogen chloride is consumed in the reaction, only very small amounts, if any, of hydrogen chloride need be fed once the reaction has been initiated if provision is made for recycle of the hydrogen chloride.

Contact time is not a critical variable and may vary from about 1 to about 30 seconds. Preferably, contact times from about 5 to about 20 seconds are used.

Reaction temperature is a critical factor. The temperature must be maintained above about 490 C. to effect the reaction. Generally, a suitable temperature range for the reaction is that from 500 to 650 C. At too high temperatures, carbon begins to deposit on the catalyst. Preferably, the temperature of the reaction is maintained from about 550 C. to about 625 C.

The process is preferably carried out .at atmospheric pressure. Either superatmospheric or subatmospheric pressures can be employed, however, although no advantages seem to be gained by their use.

What is claimed is:

1. A process for the production of ethylene which comprises contacting ethane, hydrogen chloride and oxygen in a mole ratio in the range from about 1:0.5:0.2 to 1:221 with activated alumina at a temperature from about 500 to about 650 C.

2. A process for the production of ethylene which comprises contacting ethane, hydrogen chloride and oxygen in a mole ratio of 121:0.3 at a temperature within the range from about 550 to about 625 C. with activated alumina.

3. A process for the production of ethylene which comprises passing ethane, hydrogen chloride and oxygen in a mole ratio of 1:1:0.3 through a fluidized bed of activated alumina maintained at av temperature in the range from about 500 to about 650 C. by introducing hydrogen chloride admixed with oxygen into the bottom of said bed While injecting ethane into said bed at a point which is from about 5% to about 20% of the reactor length above the bottom of said bed.

References Cited by the Examiner UNITED STATES PATENTS 2,397,638 4/1946 Bell et a1. 260-683 2,921,101 1/1960 Magovern 260-680 3,207,806 9/1965 Bajars 260680 DELBERT E. GANTZ, Primary Examiner. G. E. SCHMITKONS, Assistant Examiner. 

1. A PROCESS FOR THE PRODUCTION OF ETHYLENE WHICH COMPRISES CONTACTING ETHANE, HYDROGEN CHLORIDE AND OXYAND OXYGEN IN A MOLE RATIO IN THE RANGE FROM ABOUT TO 1:2:1 WITH ACTIVATED ALUMINA AT A TEMPERATURE FROM ABOUT 500* TO ABOUT 650*C. 